Acrylonitrile polymers dissolved in solvent mixtures comprising ethylene sulfite



ACRYLONITRHE POLYMERS DISSOLVED IN SOL- VENT MIXTURES CGMPRISING ETHYLENE SULFITE Hobson D. De Witt, Decatur, Ala., assignor to The Chemstrand Corporation, Decatur, Ala, a corporation of Delaware No Drawing. Application December 13, 1954, Serial No. 475,001

13 Claims. (Cl. 26029.6)

This invention relates to a new method of preparing synthetic fibers from polymers of acrylonitrile. More particularly, the invention relates to a new solvent material for acrylonitrile polymers, and to completely miscible mixtures including acrylonitrile polymers, from which mixtures quality fibers can be extruded.

It is well-known that polymers of over 70 percent acrylonitrile are capable of being fabricated into highstrength fibers. The conventional technique for preparing fibers from these polymers involves the dissolution of the polymer in a suitable solvent and thereafter extruding the viscous solution so prepared through an orifice into a medium which removes the solvent and precipitates the acrylonitrile polymer in a continuous form. Many solvents have been proposed, but many of them are impracticable due to the various disadvantages possessed by them such as excessive cost, poor color, tendency of the solution to gel upon standing or cooling, etc.

The primary purpose of this invention is to provide new solvent materials for the preparation of synthetic fibers which form lighter colored mixtures or solutions of acrylonitrile polymers. A further purpose of this invention is to provide a new solvent material which forms more stable mixtures of solutions of these polymers. A further purpose of the invention is to provide a new lowcost solvent for the preparation of synthetic fibers. A still further purpose of the invention is to provide a method of forming lighter colored fibers of high tensile strength and desirable elongation.

I have now discovered that mixtures of ethylene sulfite and one of the members selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide and moist nitromethane are excellent solvents for acrylonitrile polymers containing 70 percent or more of acrylonitrile and that the resulting stable solutions are lighter colored than those of earlier solvents and are particularly adapted to commercial spinning operations to produce lighter colored fibers and filaments possessing superior physical characteristics.

I have further found that acrylonitrile polymers are soluble in the above-described mixed solvents when the solvent mixtures contain not less than 50 percent of a member selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide and moist nitromethane. Solvent mixtures containing more than 50 percent proportion of ethylene sulfite do not readily dissolve acrylonitrile polymers and a sufficiently viscous solution for spinning purposes cannot be obtained. On the other hand, the proportion of ethylene sulfite contained in the solvent mixture should not be less than about ten percent in order to realize the eifect of lighter colored solutions and fibers resulting from these solutions. I there fore prefer to employ as mixed solvents mixtures containing from about 50 percent to about 85 percent of a member .selected from the group consisting of any N,N-dimethylacetamide, N,N-dirnethylformamide, and moist nitromethane and from about 15 to about 50 percent ethylene sulfite. Throughout this specification and the States Patent appended claims, the term moist nitromethane is understood to refer to nitromethane containing from about 0.5 percent to about 3.0 percent water. Anhydrous nitromethane, whether or not it is mixed with ethylene sulfite, is not a solvent for acrylonitrile polymers.

The above-described mixtures of ethylene sulfite with a member selected from the group consisting on N,N- dimethylacetamide, N,N-dimethylformamide and moist nitromethane are particularly useful as solvents for acrylonitrile polymers because solutions produced by the use of such solvents are of distinctly lighter color than those produced through the use of any of the presently known solvents. As a result, fibers produced from these solutions are lighter in color than any produced heretofore. Since the acrylonitrile polymers dissolve slowly at room temperature in any of the above-described mixtures, gradual heating is desired to secure more rapid dissolution of the polymers. Gradual heating of a mixture of one of the above-described mixtures and acrylonitrile polymers to from about to about 100 C. produces solutions of desirable viscosity ranges, and the solutions so prepared can be cooled to room temperature and below for extended periods of time without the formation of gels or precipitation of the dissolved polymer.

While mixtures of ethylene sulfite with a member selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide or moist nitromethane are excellent solvents for copolymers of or more percent of acrylonitrile and up to 30 percent of other polymerizable monomers, the invention is particularly useful with polymers of acrylonitrile containing at least percent acrylonitrile and up to 15 percent of another polymerizable monomer. The other monomers in the acrylonitrile copolymer may be vinyl acetate and other vinyl esters of monocarboxylic a'cids, methyl methacrylate and other alkyl esters of methacrylic acid, ethyl acrylate, and other alkyl esters of acrylic acid, methacrylonitrile, vinylidene chloride, ethyl maleate and other alkyl esters of maleic acid, ethyl fumarate and other alkyl esters of fumaric acid, styrene, and other vinyl-substituted aromatic compounds, a-methyl-styrene and other isopropenyl aromatic hydrocarbons, vinyl chloride and other vinyl halides, 2-vinylpyridine, Z-methyl-5-vinylpyridine, and other vinyl-substituted heterocyclic amines, and other polymerizable monomers capable of copolymerization with acrylonitrile.

The mixtures of ethylene sulfite with one of the members selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, and moist nitromethane are also particularly useful as solvents for processing fibers from blended compositions. Since many acrylonitrile polymers are not dyeable by conventional dyeing procedures, it has been proposed to blend them with polymers capable of reacting chemically with dyestuffs, whereby the mixed compositions acquire dyeability such that the fibers have general purpose utility. Suitable blending agents are the polymeric compositions of polymerizable monomers containing tertiary amino radicals or other radicals capable of being converted into tertiary amino groups subsequent to the polymerization. Thus, copolymers of vinylpyridines, for example 2-vinylpyridine, the alkyl vinylpyridines, for example 2-methyl- S-vinylpyridine, the various vinylquinolines and alkyl-substituted vinylquinolines, the various vinylpyrazines and alkyl-substituted vinylpyrazines and various vinyloxazoles and imidazoles including N-vinylimidazoles and vinylbenzimidazoles, are useful. Similarly, related allyl and methallyl derivatives of the above compounds are useful. The vinyl, allyl, and methallyl haloacetates can be reacted with secondary amines either before or after polymerization, and the polymers formed thereof blended with non-dyeable acrylonitrile polymers to develop dye afiinity. These dyeable blending polymers may be homopolymers or they may be copolymers with any monomer polymerizable therewith, for example, acrylonitrile, styrene, vinyl chloride, vinylidene chloride, and vinyl acetate. In blending the polymers, a substantial proportion of the fiber-forming acrylonitrile polymer, for example, 75 to 98 percent, should be used, depending upon the extent of dye receptivity desired and upon the proportion and relative effectiveness of the reactive monomer present. For example, a suitable blending polymer is one containing ten to 70 percent by weight of acrylonitrile and 30 to 90 percent by weight of a vinylpyridine or an alkyl-substituted vinylpyn'dine. Suitable blended compositions are those containing at least 75 percent by weight of acrylonitrile based on the total polymerized monomers in the blend. In general, from two to ten percent of the total of all polymerized monomers presout should be the dye-reactive component. The same increased dye affinity may also be achieved by the formation of terpolymers of acrylonitrile, a copolymerizable monomer, and a copolymerizable dye-reactive component. In general, I prefer to employ terpolymers of from about 85 to 95 percent acrylonitrile, from about three to eight percent of a compound selected from the group consisting of vinylpyridines and alkyl-substituted vinylpyridines, and from about two to seven percent of one of the above-named monomers copolymerizable With acrylonitrile.

All of the polymeric materials described above, both polymers and blends, are soluble in mixtures of ethylene sulfite and one of the members selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, and moist nitromethane at temperatures from about 50 to about 100 C., and solutions prepared byv so heating a mixture of the polymeric material and the solvent material are stable at room temperatures and below to give light colored fluid solutions completely free of gel formation or polymer precipitation.

In the practice of this invention, as it is in the preparation of all acrylonitrile fibers, the molecular weight or" the polymer is of critical importance. The polymer should have a molecular weight in excess of 10,000, and preferably in excess of 25,000. These molecular weights are determined by measuring the viscosity of the polymer when dissolved in a suitable solvent, such as N,N- dimethylformamide, in a manner well-known to the art. It is also very desirable to use acrylonitrile polymers which are substantially uniform throughout with respect to the chemical composition and physical structure. Such uniform polymers enable the practice of the invention more economically, permitting the utilization of continuous, uninterrupted spinning and greatly minimizing fiber fractures and clogging of the spinnerets.

In the practice of this invention, the polymers of acrylonitrile are used in finely divided form. Although massive polymers may be ground to desired particle size, preferably solvent-non-solvent polymerization procedures are employed in the preparation of the polymer. The sub-divided states of the polymers obtained by spray drying the emulsions or by filtration and subsequently drying of the solid polymers enable them to be used directly. The finely divided polymer is mixed with one of the mixed solvents containing ethylene sulfite and a member selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide and moist nitromethane in any mixing device such as dough mixer or a homogenizer. It is desirable to use a solution of as high a concentration of the polymer as possible but the maximum concentration is dependent upon the molecular weight of the polymer.

To obtain fibers of optimum physical properties, polymers of molecular weight in excess of 25,000 are used, and when using such polymers it is only possible to dissolve from about five to about 35 percent in the abovenamed mixed solvents without exceeding the practical viscosity values. Although as low as five percent of the polymer can be used in spinning operations, such concentrations are undesirable because they necessitate the removal and recovery of too much solvent from the extruded solution, thereby increasing solvent recovery costs and reducing spinning speeds by reason of the longer periods required for coagulation. The concentration of the polymer in the solution is preferably between about seven and 20 percent but will ultimately be determined by considering the desired physical properties of the fiber and the speed of spinning, which speed is a function of the concentration and viscosity of the polymer solution. The viscosity will depend upon the chemical composition and molecular weight of the polymers. The optimum proportions can thus be determined by selecting a uniform molecular weight polymer having good fiber-forming properties and dissolving it in the smallest amount of one of the mixed solvents necessary to form a viscous solution capable of extrusion at convenient temperatures.

The solution of the acrylonitrile polymer in one of the mixed solvents is extruded through an orifice or spinneret having a plurality of orifices, into a medium which re moves the solvent. The volume of the solution passing through the spinneret per unit of time must be constant in order to produce a fiber of uniform size. This is best achieved by using a positively driven gear pump constructed of corrosion-resistant metals, such as stainless steel, and adapted to deliver a constant flow of solution regardless of minor changes in viscosity and regardless of the resistance offered by the spinneret. It is also desirable to pass the solution through one or more filters before reaching the spinneret in order to remove all possible traces of foreign matter and particles of incompletely dissolved polymer. The polymer solution may be delivered to the gear pump by means of pressure applied by an inert gas to the liquid surface of the solution reservoir. The gear pump, filter devices, and conduits in the spinneret are preferably heat insulated. The extruding operation is preferably conducted at slightly elevated temperatures, but far enough below the boiling point of the solvent mixture to prevent bubbles or other irregularities in the fiber.

The medium into which the solution is extruded and which removes the solvent mixture may be either liquid or gaseous. The method involving the use of liquids is known as wet spinning; and any liquid which is nonsolvent for the acrylonitrile polymer, which either dissolves the solvent mixture used or converts it into soluble compounds, may be used. The solvent mixture is leached out of the stream of polymer solution, which first becomes a viscous stream and finally a solid filament.

When a spinneret with a plurality of apertures isused,

the several streams of polymer converge and ultimately form a single strand or tow. The spin bath must necessarily be of sufiicient size to permit the complete, or substantially complete, removal of the solvent mixture of ethylene sulfite and one of the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, and moist nitromethane. The rapidity of extrusion will effect the size of the spin bath, high speeds requiring much longer baths. The temperatures of the bath also eifect the size, high temperature permitting more rapid defusion of the solvent mixture from the fiber and enabling the use of shorter baths.

The use of solvent mixtures consisting of ethylene sulfite and one of the member selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, and moist nitromethane as solvents for acrylonitrile polymers can be adapted to dry spinning operations, wherein air, steam, nitrogen or other gas, or mixtures of gases which are inert at the spin temperature are used to remove the solvent mixture. This method operates at higher temperatures; and the solvent mixture is evaporated from the surface of the fiber. The maximum temperature to which the fibers can be Subjected is usually the boiling point of the solvent mixture used,- but to prevent the degradation of the acrylonitrile poly mer operation at lower temperatures is desirable. The fiber may be heated by convection from the hot gaseous 5 medium or by radiation from the walls of the spinning cell. Generally a combination of both convection and radiation is involved, but methods involving principally radiation are generally more efficient and permit operation with the wall temperatures considerably higher than the temperature on the surface of the fibers. The evaporation of the solvent mixtures from the fiber surface and the speed of the fiber prevent the development of a temperature exceeding that at which the fiber is stable to decomposition. The dry spinning method is particularly useful at high rates of extrusion.

In general, the methods of both wet and dry spinning commercially used are adaptable for spinning from my new solvent mixtures, but special considerations may be involved due to the different chemical nature of the solution containing ethylene sulfite. Automatic machinery for spinning continuously, drying the thread .if necessary, and winding it on suitable spools may be modified with the teaching of this specification. As in the case of most synthetic fibers, the fibers of acrylonitrile copolymers spun from solutions in my new solvent mixtures may be stretched to develop optimum physical properties. i desired, part of the necessary stretching may be accomplished in the spinning medium by drawing the fiber out of the bath at a rate more rapid than the rate of extrusion.

The following examples in which parts, proportions, and percentages are by weight illustrate further the applications of the principles of this invention.

bath such as water or a lower alcohol to yield fibers and films.

Example 11 A mixture of 25 parts of moist nitromethane containing one percent water and five parts ethylene sulfite was prepared which dissolved three parts of a copolymer of 94 percent acrylonitrile and six percent vinyl acetate within 15 minutes at 80 C. with stirring. The clear, viscous solution which resulted was stable on cooling to room temperature and was suitable for extrusion into a nonsolvent coagulating bath to yield fibers and films.

Example 111 One part of a blend of 88 percent of a copolymer of 94 percent acrylonitrile and six percent vinyl acetate and 12 percent of a copolymer of percent acrylonitrile and 50 percent Z-methyl-S-vinylpyridine was dissolved in 19 parts of each of the solvent mixtures set out in the table below by stirring for 15 minutes at 80 C.

N ,N -Dimethylacetamide, ml.

Ethylene Sulflte, ml.

Percent Ethylene Sulfite All the solutions obtained were clear, viscous and suitable for extrusion into a non-solvent coagulating bath to yield fibers and films.

Example IV One part of a blend of 88 percent of a copol yrner of 94 percent acrylonitrile and six percent vinyl acetate and 12 percent of a copolymer of 50 percent acrylonitrile and 50 percent 2-methyl-5-vinylpyridine was dissolved in 19 parts of solvent mixture of 25 percent ethylene sulfite in N,N-dimethylacetamide at C. A similar solution of one part of the same blended polymer was made in 19 parts of N,N-dimethylacetamide alone at 80 C. Both solutions were held at 80 C. for two hours, and the colors of the solutions compared at the end of this period. It was found that the solution of polymer in the mixed solvent had developed appreciably less color than had the solution of lLN-dimethylacetamide alone.

Example V There was dissolved 3.3 parts of polyacrylonitrile in 22 parts of a solvent mixture of 32 percent ethylene sulfite in N,N-dirnethylacetamide at 100 C. with stirring. The resulting 13 percent solution was clear, viscous and suiticiently fluid for readily extruding into a non-solvent coagulating bath to yield fibers and films.

I claim:

1. A new composition of matter comprising a homogenous miscible mixture of a solvent mixture of from about ten to about 50 percent ethylene sulfite and from about 50 to about percent of a compound selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylrormamide and nitrornethane containing 0.5 to 3.0 percent water, and a polymer of which acrylonitrile is at least 70 percent of the total polymerized monomer content.

2. A new composition of matter comprising a homogenous miscible mixture of from 65 to 'percent by weight of a mixture of from about 50 percent to about 90 percent of a compound selected from the group consisting of N,N- dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of a polymer of which acrylonitrile is at least 70 percent of the total polymerized monomer content.

3. A new composition of matter comprising a homogenous miscible mixture of from 65 to 95 percent by weight of a mixture of from about 50 percent to about 90 percent of a compound selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylforamide and moist nitromethane and from about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of a polymer of at least about 70 percent acrylonitrile and up to about 30 percent of another copolymerizable monomer.

4. A new composition of matter comprising a homogenous miscible mixture of from 65 to 95 percent by weight of a mixture of from about 50 to about 90 percent of a compound selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of a polymer of at least about 70 percent acrylonitrile and up to about 30 percent vinyl acetate.

5. A new composition of matter comprising a homogenous miscible mixture of from 65 to 95 percent by weight of a mixture of from about 50 to about 90 percent of a compound selected from the group consisting of N,N- dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of a polymer of at least about 70 percent acrylonitrile and up to about 30 percent vinylpyridine.

6. A new composition of matter comprising a homogenous miscible mixture of from 65 to 95 percent by weight of a mixture of from about 50 to about 90 percent of a compound selected from the group consisting of N,N- dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from I about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of polyacrylonitrile.

7. A new composition of matter comprising a homogenous miscible mixture of from 65 to 95 percent by weight of a mixture of from about 50 to about 90 percent of a compound selected from the group consisting of N,N- dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of a blend (A) a copolymer of at least 75 percent acrylonitrile and up to 25 percent of another copolymerizable monomer and (B) a copolymer of from 30 to 90 percent of a compound selected from the group consisting of vinylpyridines and alkyl-substituted vinylpyridines and from ten to 70 percent of another copolymerizable monomer.

8. A new composition of matter comprising a homogenous miscible mixture of from 65 to 95 percent by weight of a mixture of from about 50 to about 90 percent of a compound selected from the group consisting of N,N- dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite, and from five to 35 percent of a blend of (A) a copolymer of at least 75 percent acrylonitrile and up to 25 percent vinylacetate and (B) a copolymer of from 30 to 90 percent of a compound selected from the group consisting of vinylpyridines and alkyl-substituted vinylpyridines and from ten to 70 percent by weight of acrylonitrile.

9. A new composition of matter comprising a homogcnous miscible mixture of a solvent mixture of from about 50 percent to about 90 percent of a compound selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent Water and from about ten to about 50 percent of ethylene sulfite, and a terpolymer containing by weight in the polymer molecule from 85 to 95 percent acrylonitrile, from three to eight percent of the compound selected from the group consisting of vinylpyridines and alkyl-substituted vinylpyridines, and

'8 from two to seven percent of another polymerizable monomer.

10. A process of preparing a fiber-forming solution comprising mixing a polymer of which acrylonitrile is at least 70 percent of the total polymerized monomer content with a solvent mixture of from about to about 90 percent of a compound selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide and nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite and heating to a temperature of from about to about 100 C. until the polymer is dissolved therein.

11. A process of preparing a fiber-forming solution comprising mixing a polymer of which acrylonitrile is at least percent of the total polymerized content with a solvent mixture of from about 50 percent to about percent of N,N-dimethylacetamide and from about ten to about 50 percent of ethylene sulfite and heating to a temperature of from about 65 to about C. until the polymer is dissolved therein.

12. A process of preparing a fiber-forming solution comprising mixing a polymer of which acrylonitrile is at least 70 percent of the total polymerized monomer content with a solvent mixture of from about 50 percent to about 90 percent of N,N-dimethylformamide and about ten percent to about 50 percent of ethylene sulfite and heating to a temperature of from about 65 to about 100 C. until the polymer is dissolved therein.

13. A process of preparing a fiber-forming solution comprising mixing a polymer of which acrylonitrile is about 70 percent of the total polymerized monomer content with a solvent mixture of from about 50 to about 90 percent of nitromethane containing 0.5 to 3.0 percent water and from about ten to about 50 percent of ethylene sulfite and heating to a temperature of from about 65 to about 100 C. until the polymer is dissolved therein.

No references cited. 

1. A NEW COMPOSITION OF MATTER COMPRISING A HOMOGENOUS MISCIBLE MIXTURE OF A SOLVENT MIXTURE OF FROM ABOUT TEN TO ABOUT 50 PERCENT ETHYLENE SULFITE AND FROM ABOUT 50 TO ABOUT 90 PERCENT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF N,N-DIMETHYLACETAMIDE. N,N-DIMETHYLFORMAMIDE AND NITROMETHANE CONTAINING 0.5 TO 3.0 PERCENT WATER, AND A POLYMER OF WHICH ACRYLONITRILE IS AT LEAST 70 PERCENT OF THE TOTAL POLYMERIZED MONOMER CONTENT. 